Apparatus for directing a light beam

ABSTRACT

Apparatus for directing a light beam in a desired direction without moving the light source. An optical system is disclosed, including a laser and a linearly translatable optical device for directing or orienting a beam from the laser. The optical directional device includes a series of mirrors arranged to successively reflect the laser beam and further includes structure for rotating the mirrors about various axes to allow exiting of the laser beam from the last of these mirrors in a desired direction. The laser system is particularly useful in the process of photocoagulation and is useful in other medical and optical applications as well.

United States Patent Swope [54] APPARATUS FOR DIRECTING A LIGHT [1513,653,384 [4 1 Apr. 4, 1972 3,528,424 9/1970 Ayres ..l28/303.l

Primary Examiner-L. W. Trapp Attorney-William C. Nealon, Noble S.Williams, Robert 1. Bird and Bernard L. Sweeney [5 7] ABSTRACT Apparatusfor directing a light beam in a desired direction without moving thelight source. An optical system is disclosed, including a laser and alinearly translatable optical device for directing or orienting a beamfrom the laser. The optical directional device includes a series ofmirrors arranged to successively reflect the laser beam and furtherincludes structure for rotating the mirrors about various axes to allowexiting of the laser beam from the last of these mirrors in a desireddirection. The laser system is particularly useful in the process ofphotocoagulation and is useful in other medical and optical applicationsas well.

9 Claims, 3 Drawing Figures Patented April 4, 1972 2 Sheets-Sheet lINVENTOR. CHARLES HERMAS SWOPE BY @yw ATTORNEY Patented April 4, 19723,653,384

2 Sheets-Sheet 8 INVENTOR.

HORIZONTAL h CHARLES HERMAS SWOPE F E 3 ATTORNEY BY m w BACKGROUND OFTHE INVENTION 1. Field of the Invention The present invention relates toapparatus for directing light energy in a desired direction withoutmoving the light source. More particularly, it relates to aphotocoagulation system which utilizes a stationary laser and apparatusfor translating and rotating a reflected beam from said laser which isdirected from the photocoagulation system upon the surface of livingtissue to cause coagulation.

2. Description of the Prior Art In Us. Pat. No. 3,084,694 to Kavanagh etal., entitled Photocoagulation Apparatus, and in US. Pat. No. 3,348,547to Kavanagh entitled Photocoagulating Apparatus (both patents beingassigned to the assignee of the present invention), prior art isdescribed. Material disclosed in these patents is incorporated herein byreference.

There are limitations in this prior art. For example, disclosedapparatus for directing a beam of light is limited in its range ofexiting beam angular orientation, and other limitations will becomeapparent after reviewing these two patents.

Other known methods for photocoagulation incorporate a large, mobilegas-laser. A problem associated therewith (and which the presentinvention solves) is misalignment of the laser beam and the opticaltrain, when the optical train is moved. The present invention describesapparatus for allowing the laser to remain motionless while readilymaintaining beam alignment to the optical train as the optical train iseasily moved. Prior art further includes an optical device known as anarticulated arm. This device has been fabricated and sold by theassignee of the present invention. The articulated arm uses sevensuccessively reflecting mirrors, arranged so that the light beamreflected from the last mirror can be pointed in some desired direction.The articulated arm is a prior art solution for maintaining a laserstationary in a photocoagulation system. However, the articulated arm isrestricted in its usefulness, one of the reasons being that the arm haslimited length.

Among other disadvantages of the articulated arm are the relativelylarge number of mirrors required which presents compounded alignmentproblems. Also, the arm structure itself imposes the constraint ofcurvilinear motion of the beamexit aperture for certain arm positions,and this prevents perpendicular penetration of the beam into a surfacefor finite sideways displacements of the beam. This is a limitation incertain delicate photocoagulating operations.

The articulated arm necessarily is large and requires complex supportingstructure with careful counterbalancing in order for it to workproperly. The arm cannot support a heavy optical system. Furthermore,the device is difficult to fabricate and assemble, and is relativelyexpensive to manufacture.

The present invention is an improvement over the articulated arm andother prior art. The present invention in a preferred embodiment usesonly three mirrors. The optical alignment procedure is uncomplicated.There are no gear reductions used in the apparatus of the presentinvention as is found in some old techniques. The translational motionof the apparatus is essentially unlimited-(limited only by the length ofparallel guide rails used to guide the translational motion of theapparatus).

' SUMMARY OF THE INVENTION The present invention relates to apparatusfor directing a beam of light emitted from a laser or from otherappropriate light emitting devices. More specifically, the apparatusdirects a light beam usually nominally collimated via a series of threemirrors that successively reflect the beam so that it exits in a desireddirection. One mirror utilizes translational motion and the other twomirrors utilize rotational motions.

Each of the two rotational motions are about different axes each beingparallel to, or colinear with, a reflected light beam. Parallel ishereby defined to include colinear. There is a first rotation about avertical axis and a second rotation about a horizontal axis. These tworotations in themselves allow sufficient freedom of movement to aim alight beam in almost any direction. The additional freedom oftranslational motion is in a direction parallel to a primary beam whichemerges from a light source. It permits a linear beam movementpreviously unavailable in photocoagulators utilizing other reflectivearrangements.

The three mirrors are so arranged in an illustrative embodiment of thepresent invention that the light beam reflected from any mirror makes anangle of 90 with the light beam incident to that particular mirror. Arotation of a mirror about an axis that is parallel or colinear with alight beam incident thereupon, does not disturb the aforementioned 90angular displacement relationship between incident and reflected beam.This 90 relationship is not essential to the operation of the presentinvention; i.e., the relationship could be 60, etc., or any other angle.However, is selected. In a particular embodiment of the presentinvention, the supporting structure is made of transparent materialthereby eliminating possible interference with the primary beamsincidence upon the first mirror.

Orienting means is provided for simultaneously rotating the secondmirror and orbiting the third mirror about an axis parallel to the firstreflected laser beam and for independently rotating the third mirrorabout an axis parallel to the second reflected beam. The apparatus isincorporated in a photocoagulation 'system wherein a rotatable fourthmirror (termed a pantographic mirror) can be utilized to provideadditional useful beam motion and to permit a physician to clearlyobserve his work with the beam in a photocoagulating operation.

Included among the advantages of the present invention are: weight ofthe system is carried by linear guide-rails allowing heavy systems to bemounted and moved without encountering large torques associated withprior art devices; distances between mirrors in a specific embodimentare variable and adjustable permitting minimization of unwanted torqueor translations between mirrors; mass of optical coupling which mayrequire movement is smallhence inertia is small and balance of theoptical apparatus does not change much for movement over an entirerange; and, mirrors are used in full reflection only, thereby making theapparatus wavelen gth independent over the visible spectrum.

The present invention is not intended to be limited to photocoagulationsystems. Any application which calls for directing a beam, preferablycollimated, from a stationary source into a moveable optical systemwould usefully incorporate the present invention.

Thus, it is an object of the paratus for directing a beam almost anydesired direction.

It is a further object of the present invention to provide an improvedphotocoagulation system.

Other objects and advantages of the present invention will becomeapparent to one having reasonable skill in the art after referring to adetailed description of the appended drawings wherein:

present in vention to provide apof light, preferably collimated, in

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partly broken awayperspective view of a particular embodiment of the present invention,showing a primary laser beam input thereto and directionally reflectedoutput beam therefrom. Only one of the three mirrors that are utilized,can be seen;

FIG. 2 is another partly broken away perspective view of a particularembodiment of the present invention showing a detailed arrangement ofthe three successively reflecting mirrors and their respective mountingstructures; and,

FIG. 3 is an optical-schematic diagram showing a particular orientationof the successive reflective arrangement of the three mirrors whereinthe impinging primary beam, the first reflected beam, the secondreflected beam, and the third reflected beam all lie in the same plane.Also depicted are the 90 angular displacements between incident andreflected beams for each of the three mirrors, and the directions ofmotions available to the apparatus.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 depicts laser 31emitting primary laser beam 13 in a direction to mirror 11. Mirror 11 issupported by cylindrical member 38 fixed to slideable base 34. Slideablebase 34 is arranged to translate on guide rails 33, in directions 30parallel to primary beam 13. First reflected beam 16 reflected frommirror'll, is directed vertically upward into (and co-axially with)hollow rod 40 and is incident upon a second mirror (not shown). Uponreflection from the second mirror and successive incidence andreflection from a third mirror (not shown) the third reflected beampasses through optical processor 37 (where it is collimated, etc.) andis emitted as third reflected beam 26.

Rotatable base 35 is arranged to rotate in directions 33 and rotatesrelative to slideable base 34. Constrained to rotate with rotatable base35 are the following: vertical support members 36, pins (only one shown)39, second and third mirrors (not shown), movable platform 32, opticalprocessor 37, hollow rod 40, and horizontal support bar 41. Movableplatform 32 is further arranged to rotate in directions 24. Constrainedto rotate with platform 32 are: pin 39, optical processor 37, and athird mirror (not shown) supported within movable platform 32.

In FIG. 2 a second mirror 17 is supported by hollow cylindrical rod 40and third mirror 22 is supported by mounting device 42 attached tomovable platform 32 as shown. The axis of rotation of pins 39 is theaxis of rotation of third mirror 22. Mounting device 42 swings beneaththis axis. Mirrors l1, l7 and 22 are all visible in FIG. 2.

In operation one should consider FIGS. 1 and 2 in conjunction with FIG.3 wherein mirrors ll, 17 and 22 are arranged schematically. In FIG. 3which depicts a unique situation for purposes of clarity of illustrationin which all beams lie in the same plane, primary beam 13 impinges onmirror 11 which is oriented to provide an angle of 90 at reflectivesurface 12 between primary beam 13 and first reflected beam 16.

First reflected beam 16 impinges upon mirror 17 which is oriented toprovide a 90 displacement between first reflected beam 16 and secondreflected beam 25 at reflective surface 19. Mirror 17 rotates indirection 23.

Second reflected beam 25 impinges on mirror 22 which is oriented toprovide a 90 angular displacement between second reflected beam 25 andthird reflected beam 26 at reflective surface 21. Mirror 22 is rotatablein direction 24. These angular displacements need not be 90 as will beexplained below.

In order to aim exiting beam 26 in a desired direction, one rotatesmirrors 17 and 22. If one rotates mirror 22 through an angle of 360 (indirection 24) while simultaneously maintaining mirrors 17 and I1 fixed,one provides an exiting beam 26 whose locus defines a vertical planeseen on edge in FIG. 3. (Note reference plane 50, a horizontal planeseen on edge).

By comparison, if one rotates mirror 17 in direction 23 through 360 (andthereby orbits mirror 22)but does not rotate mirror 22 in direction 24,while maintaining mirror 11 fixed with respect thereto, the locus ofexiting beam 26 defines a cylindrical surface of radius equal to thelength of second reflected beam 25.

If mirrors 17 and 22 are both rotated simultaneously (but notnecessarily at the same frequency) and if one could take a long exposurethree dimensional photograph of exiting laser beam 26, one would observea cylindrical hole within the laser light of radius equal to the lengthof second reflected beam 25. The laser light provided by motion ofmirrors 17 and 22 would thus leave a cylindrical hole in the photographwherein the laser beam does not penetrate.

However, this hole is fllled by beam 26 for sufficient motion of mirror11 in a linear direction. It is seen that when mirror 11 is movedthrough a distance equal to twice the distance of'second reflected beam25, (the diameter of the cylindrical hole referred to above) there is nospace left unpainted" by the exiting laser beam. Thus, the three motionsallow impingement of the beam on all points in space, (for example, onall points comprising the inside surface of a room). This latterstatement is true provided that the structure of the device itself doesnot interfere with primary laser beam 13 from impinging on mirror 11.

In order that the supporting structure of the present invention does notinterfere with primary beam 13, a particular embodiment utilizes astructure made of a transparent material such as glass. Thus, no part ofthe supporting structure can interfere with primary beam 13 impinging onmirror 11. It is for this embodiment that exiting beam 26 can be pointedin almost any desired direction. For most supporting structures not madefrom transparent glass, exiting beam 26 is more limited in its angularorientation. In principle, the beam can be pointed in every direction,and is only limited by the design of the supporting structure.

An alternative embodiment suspends mirror 11 below the structure. Thislocation of mirror 1 l prevents self-interference by the structure. Inthis embodiment the structure need not necessarily be transparent toprovide the same degree of direction-selection as with transparentmaterial.

It should be apparent to one skilled in the art that rotating meansdisclosed herein need not be manually operated. For example, rotatablebase 35 and pin 39 could be motor driven. They could be motor controlledto position the exiting beam at a desired angle. A similar arrangmentcould be used in a motor driven periscope, wherein this periscope wouldhave an additional feature of angular elevation control, rather thanonly horizontal plane scanning capability. In a periscope application,the direction of light passing through the present invention wouldmerely be reversed so that the entering beam would then be beam 26 andthe exiting beam would then be beam 13.

It is to be understood that in yet another embodiment the distancesbetween adjacent mirrors are not necessarily fixed distances, but aremade variable, utilizing appropriate adjustment means.

In some applications, telescopic (translational) motions between mirrors1] and 17 and/or mirrors l7 and 22 may be desirable. These motions areparallel to the respective reflected beams. The distances betweenmirrors are arbitrary and in principle, the distance between mirrors canbe made as large as desirable.

In photocoagulation applications, a pantographic mirror (not shown) canbe mounted on the output of optical processor 37 which further providesa 2:1 reduction in angle (an angular displacement of a mirror of 10gives a change in beam angle of 20 These pantographic mirrors can bepartly transmissive and provide a physician with means for viewing(parallel to the exiting beam) the effect of his laser beam surgery uponthe retina of a human eye or upon other body tissues.

The invention may be embodied in yet other specific forms withoutdeparting from the spirit or essential characteristics thereof. Forexample, many optical systems can be connected in tandem whereby a laserbeam output from one system supplies the laser beam input to the nextsuccessive optical system. The present embodiments are therefore to beconsidered'in all respects as illustrative and not restrictive, thescope of the invention being indicated by the appended claims ratherthan by the foregoing description, and all changes which come within themeaning and range of equivalency of the claims are therefore intended tobe embraced therein.

I claim:

1. A laser system of a type capable of use in a photocoagulatorincluding a laser and linearly translatable directional means fordirecting a primary beam from said laser, said directional meanscomprising:

a supporting structure;

a series of mirrors supported by said structure, said mirrors arrangedto successively reflect said beam; and,

orienting means for orienting said mirrors to allow exiting of said beamfrom the last of said mirrors in a desired direction.

2. A system as recited in claim 1 wherein said series of mirrors furthercomprises:

a first mirror supported by said structure said first mirror arranged toreflect said primary beam incident thereupon providing a first reflectedbeam;

a second mirror supported by said structure, said second mirror arrangedto reflect said first reflected beam incident thereupon, providing asecond reflected beam; and

a third mirror supported by said structure, said third mirror arrangedto reflect said second reflected beam incident thereupon, providing athird reflected beam exiting from said system.

3. A system as recited in claim 2 wherein said orienting means comprisesmeans for simultaneously rotating said second mirror and orbiting saidthird mirror about an axis parallel to said first reflected beam, andfor independently rotating said third mirror about an axis parallel tosaid second reflected beam, whereby said exiting third beam is pointedin a desired direction.

4. A system as recited in claim 3 further including'a motor wherein saidorienting means is operatively connected to said motor.

5. A system as recited in claim 2 wherein said second mirror is arrangedto angularly displace said second reflected beam by substantially fromsaid first reflected beam and said third mirror is arranged to angularlydisplace said third reflected beam by substantially 90 from said secondreflected beam.

6. A system as recited in claim 2 wherein said first reflected beam isangularly displaced from said primary beam by substantially 90.

7. A system as recited in claim 2 wherein said first mirror is displacedfrom said second mirror by a first selectable distance.

8. A system as recited in claim 2 wherein said first mirror is displacedfrom said third mirror by a second selectable distance. i

9. A system as recited in claim 1 wherein said structure is made ofmaterial transparent to said primary beam.

1. A laser system of a type capable of use in a photocoagulatorincluding a laser and linearly translatable directional means fordirecting a primary beam from said laser, said directional meanscomprising: a supporting structure; a series of mirrors supported bysaid structure, said mirrors arranged to successively reflect said beam;and, orienting means for orienting said mirrors to allow exiting of saidbeam from the last of said mirrors in a desired direction.
 2. A systemas recited in claim 1 wherein said series of mirrors further comprises:a first mirror supported by said structure said first mirror arranged toreflect said primary beam incident thereupon providing a first reflectedbeam; a second mirror supported by said structure, said second mirrorarranged to reflect said first reflected beam incident thereupon,providing a second reflected beam; and a third mirror supported by saidstructure, said third mirror arranged to reflect said second reflectedbeam incident thereupon, providing a third reflected beam exiting fromsaid system.
 3. A system as recited in claim 2 wherein said orientingmeans comprises means for simultaneously rotating said second mirror andorbiting said third mirror about an axis parallel to said firstreflected beam, and for independently rotating said third mirror aboutan axis parallel to said second reflected beam, whereby said exitingthird beam is pointed in a desired direction.
 4. A system as recited inclaim 3 further including a motor wherein said orienting means isoperatively connected to said motor.
 5. A system as recited in claim 2wherein said second mirror is arranged to angularly displace said secondreflected beam by substantially 90* from said first reflected beam andsaid third mirror is arranged to angularly displace said third reflectedbeam by substantially 90* from said second reflected beam.
 6. A systemas recited in claim 2 wherein said first reflected beam is angularlydisplaced from said primary beam by substantially 90*.
 7. A system asrecited in claim 2 wherein said first mirror is displaced from saidsecond mirror by a first selectable distance.
 8. A system as recited inclaim 2 wherein said first mirror is displaced from said third mirror bya second selectable distance.
 9. A system as recited in claim 1 whereinsaid structure is made of material transparent to said primary beam.